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Effect of spinal immobilization devices on pulmonary function in the healthy, nonsmoking man
ORIGINAL CONTRIBUTION immobilization, spinal, devices; pulmonary function, effect of spinal immobilization
Effect of Spinal Immobilization Devices on Pulmonary Function in the Healthy, Nonsmoking Man In the prehospital management of trauma, a variety of devices are used for immobilization of the spinal column during extrication and transport. Two of these commonly used immobilizers, the Zee Extrication Device ® and the long spinal board, use crisscrossing straps over the thorax to affix the patient to the device. Our study was designed to determine if these two devices alter pulmonary function in the healthy, nonsmoking man. We took 15 healthy, nonsmoking male volunteers and tested four pulmonary function parameters: forced vital capacity (FVC), forced expiratory volume in one second (FEV1), the ratio FEVI:FVC, and forced mid-expiratory flow (FEF 25%-75%). A Breon spirometer was used to test these functions both before and after the volunteers were strapped into the two devices. Three separate trials were given for each parameter and the best scores were used for data computation. Strap tension was controlled by placing a sphygmomanometer beneath each strap and adding tension to produce 10 m m Hg pressure. We found a significant difference (P < .05) between prestrapping and poststrapping values for three of the four functions tested using the long spinal board: FVC (P = .0079), FEV 1 (P = .0001), and FEF 25%-75% (P = .0252). Similarly significant differences were found for three of the four parameters using the Zee Extrication Device®: FVC (P = .004), FEV 1 (P = .0022), and FEF 25%-75% (P = .008). These differences reflect a marked pulmonary restrictive effect. The ratio FEVdFVC can be normal or even slightly elevated with restrictive airway disease due to proportional reductions of each parameter. Correspondingly, we found no significant difference between prestrapping and poststrapping FEVI:FVC values (P > .05). We conclude from our data that these devices produce a significantly restrictive effect on pulmonary function in the healthy, nonsmoking man. [Bauer D, Kowalski R: Effect of spinal i m m o b i l i z a t i o n devices on p u l m o n a r y function in the healthy, nonsmoking man. Ann Emerg Med September 1988;17:915-918.]
David Bauer, MD Robert Kowalski Royal Oak, Michigan From the Department of Emergency Medicine, William Beaumont Hospital, Royal ©ak, Michigan. Received for publication August 17, 1987. Revision received April 18, 1988. Accepted for publication June 1, 1988. Presented at the University Association for Emergency Medicine Annual Meeting in Philadelphia, May 1987. Address for reprints: David Bauer, MD, William Beaumont Hospital, Department of Emergency Medicine, 3601 West Thirteen Mile, Royal Oak, Michigan 48072.
INTRODUCTION In the prehospital management of trauma, a variety of devices are used for immobilization of the spinal column during extrication and transport. Two of these commonly used devices, the Zee Extrication Device ® (ZED) (Zee Medical Products, Irvine, California} (Figure 1) and the long spinal board (Figure 2), use crisscrossing straps over the thorax to affix the patient to the device {Figures 3 and 4}. Our study was designed to determine if these two devices alter pulmonary function in the healthy, nonsmoking man because they are used universally in emergency departments, and their effect on pulmonary function may have clinical significance. No studies have addressed this particular issue. However, Abraham et all used pulmonary function tests to analyze the effects of pneumatic trousers on respiratory function, and Ranson and McSwain 2 also studied respiratory function after pneumatic trouser application but used arterial blood gas measurements. MATERIALS A N D M E T H O D S Study approval was granted by the Human Investigations Committee of William Beaumont Hospital. Study participants were 15 male volunteers 23 to 28 years old who had no history of recurrent respiratory disease, heart 17:9 September 1988
Annals of Emergency Medicine
915/91
SPINAL IMMOBILIZATION DEVICES Bauer & Kowalski
FIGURE 1. ZEE Extrication Device ®. FIGURE 2. Long spinal board.
disease, or current respiratory symptoms (ie, cough, nasal discharge, or c o n g e s t i o n ) , and w h o w e r e n o n smokers. Before participation, a brief physical examination including lung auscultation was performed, and none of the volunteers was observed to have abnormal findings. Volunteers were aware of the mechanics of the study but were not informed of its purpose. Two i m m o b i l i z a t i o n devices were tested in the study. One device, the ZED, is used c o m m o n l y in extrication when spinal immobilization is necessary. It consists of an oblong piece of durable cloth material reinforced with long, thin metal bars. Multiple crisscrossing straps affix the patient's torso to the board. The second device tested was a long spinal board routinely used for patient transport if spinal injury is suspected. It also uses crisscrossing straps across the thorax. The same two boards were used throughout the study. To test the effect of each device on pulmonary function, both control trials and poststrapping trials were conducted. Subjects were placed on each board in the supine position, and pulmonary functions were measured with a Breon spirometer. Measurements included forced vital capacity (FVC), forced expiratory v o l u m e in one second (FEV1), forced midexpiratory f l o w (FEF 2 5 % - 7 5 % ) , a n d t h e FEVI:FVC ratio. Three prestrapping trials were performed on each subject on each board. Testing was done by two respiratory therapists blinded to the purpose of the study and experienced in performing pulmonary function testing. C o a c h i n g t e c h n i q u e s were kept consistent throughout the study. A one-minute rest was allotted between each trial. Results were recorded with the spirometer on a separate piece of graph paper for each trial. After these control trials, the straps were applied to the subjects, and three trials of p u l m o n a r y functions were carried out on each board as outlined above. Strapping was done by the same investigator at all times. Strap tension was regulated by placing a s p h y g m o m a n o m e t e r bladder u n d e r each strap and applying tension until 10 m m Hg was recorded at functional
92/916
TABLE L ZEE extrication device
Parameter
Prestrapping (L/min)
Poststrapping (I./min)
P
FVC
5.41
+_ 0.81
4.78
+ 0.73
.0040
FEV~
4.43
_+ 0.67
3.95
_+ 0.59
.0022
FEF 25%-75%
4.56
+ 1.28
3.90
_+ 0.96
.0080
FEV~:FVC
0.816 _+ 0.05
0.820 _+ 0.04
.6107
Values are mean _+ SD. FVC, forced vital capacity; FEV1, forced expiratory volume in one second; FEF 25%-75%, forced midexpiratory flow; FEVcFVC, ratio of FEVt to FVC.
residual capacity (end-expiration point). This value of 10 m m Hg for strap tension was obtained before the study by having an experienced paramedic blinded to the study strap a volunteer to the board. His strap tension was recorded on three separate occasions (mean, 10 m m Hg). T h e r e s u l t s of p r e s t r a p p i n g and
Annals of Emergency Medicine
poststrapping values for both boards were derived from the graph paper recordings. R e c o m m e n d a t i o n s by the American Thoracic Society for computation of data were used. 3 For each set of three trials, the largest FVC and FEV 1 values were taken for data computation, even if they were from different recordings. Reproducibility of 17:9 September 1988
FIGURE 3. Demonstration of patient
strapped in long spinal board. FIGURE 4. Demonstration of patient strapped in ZED board. inate a c c u m u l a t i o n of Type I errors because pulmonary functions were not independent. This value was significant at P = .0287 and indicated a significant effect by the ZED or long s p i n a l board. I n d i v i d u a l S t u d e n t ' s t tests then were performed on all four p u l m o n a r y functions for each board to isolate significant effects. Finally, to determine if there was a significant difference between the ZED and the spinal boards, Hotelling's T2 m u l t i v a r i a t e analysis was applied to the m e a n vectors.
RESULTS For the ZED board, the values are shown (Table 1}. A significant effect was noted for three of the four pulmonary hmctions: FVC (P = .004), FEV 1 (P = .0022), and FEF 25%-75% (P = .008). FEVI:FVC was not affected significantly {P = .61). For the spinal board, the values are shown (Table 2). The same three pulm o n a r y f u n c t i o n s were affected by strapping: FVC (P = .0001), FEV 1 (P = .0079), and FEF 25%-75% (P = .0252). Again, FEVI:FVC was not significantly altered. N o significant difference in effect b e t w e e n t h e t w o b o a r d s was f o u n d {P = .413) (Table 3) w h e n t h e difference between prestrapping and poststrapping values of each parameter were compared.
TABLE 2. Long spinal board
Parameter
Prestrapping (L/min)
FVC
5.52
FEV 1 FEF 25%-75%
4.29
_+ 0.64
4.11
± 1.12
FEVI:FVC
0.791 ± 0.05
_+ 0.79
Poststrapping (L/min) 4.98
P
± 0.67
.0001
3.99
± 0.57
.0079
3.68
±.1.02
.0252
0.793 ± 0 . 0 5
.8541
Values are mean _+ SD.
FVC and FEV 1 was ensured because the best two of three spirograms for these parameters did not vary by m o r e than 5% of t h e largest v a l u e or b y more than 100 mL. The FEF 25%-75% values then were taken from the tracing with the largest s u m of FVC and FEV1, as r e c o m m e n d e d by the Society.3 T h e b a c k - e x t r a p o l a t i o n t e c h nique as d e s c r i b e d b y S m i t h a n d Gaensler4 was i m p l e m e n t e d to extract 17:9 September 1988
v a l u e s on r e c o r d i n g s in w h i c h t h e steepest slope of the curve did n o t occur at the onset. To determine whether either board had a significant effect (P < .05) on p u l m o n a r y function values, poststrapping values were compared w i t h prestrapping values, and Hotelling's T2 multivariate analysis of variance was performed on the m e a n vectors. This statistical m e t h o d was chosen to elim-
Annals of Emergency Medicine
DISCUSSION The results of this study indicate a restrictive effect on p u l m o n a r y function by both the ZED and the spinal boards. In r e s t r i c t i v e a i r w a y disease (ie, p u l m o n a r y fibrosis, pleuraf fibrosis, or c h e s t w a l l a b n o r m a l i t i e s ) , values for FVC are s i g n i f i c a n t l y reduced, reflecting decreased total lung v o l u m e . S u c h a n effect w a s f o u n d w i t h b o t h devices in this study. Decreases in FEV 1 are m o s t notable in obstructive airway disease, S,6 but because expiratory flow in a m a x i m a l effort is d e p e n d e n t on lung volume, FEV1 m a y be reduced w i t h restrictive abnormalities. 6 U n l i k e t h a t seen w i t h obstructive disease, however, the decrease in FEV 1 seen in restrictive conditions is pro917/93
SPINAL IMMOBILIZATION DEVICES Bauer & Kowalski
p o r t i o n a l to the d e c r e m e n t i n l u n g volume; thus, FEV 1 decreases but a normal or slightly elevated FEVI:FVC results. 6 The findings of a significant decrease in FEV I and a lack of significant change in FEVI:FVC w h e n comparing prestrapping with poststrapping values are consistent with restriction. Finally, w i t h marked restrictive disease, a r e d u c t i o n i n FEF 25%-75% may occur, although not as noticeably as in obstructive disease. Again, a significant lowering of FEF 25%-75% observed in this study is consistent with this cause. Standard p u l m o n a r y function values based on age, sex, and height have been described by various authors.g,7, s By convention, subjects in these studies were either standing or sitting, in contrast to the present study where subjects were tested supine. Nevertheless, 14 of 15 subjects tested supine in this s t u d y had b a s e l i n e p u l m o n a r y function values that were w i t h i n the a c c e p t a b l e range for age, sex, and height, as recommended by the American Thoracic Society for standing or sitting values. This includes an FVC and FEV I more than 80% of predicted values and FEF 25%-75% more than 60% of predicted values. One subject had an FVC of 79% of predicted value. Limitations of this study included study in the laboratory versus a true clinical setting, the small sample size, and an estimation of average strap tension by a b l i n d e d p a r a m e d i c ; these should be noted w h e n interpreting the results of this study. O t h e r i n v e s t i g a t o r s have o u t l i n e d the detrimental effects of the supine position on pulmonary function, presumably related to redistribution of blood flow with subsequent increased p u l m o n a r y v o l u m e . I , 9 Because the purpose of this study was to detect differences in p u l m o n a r y functions induced by these devices, subjects serving as their own controls were tested supine. The practical i m p l i c a t i o n of this is exemplified by analyzing time
94/918
TABLE 3. C o m p a r i s o n o f effect on. p u l m o n a r y
function --
L o n g s p i n a l b o a r d vs Z E D b o a r d
Parameter
Poststrapping- Prestrapping (L/min) Long Board ZED Board
P
FVC
0.532
0.635
0.523
FEV1
0.297
0.477
0.083
FEF 25%-75%
0.407
0.648
O.158
FEV1:FVC
0.002
0.004
0.608
relations i n the clinical setting regarding supine versus sitting positions. Although suspected spinal t r a u m a victims may spend a brief period in the sitting position during extrication with a ZED device, the vast majority of their time while strapped in either of these immobilizers is spent supine. This w o u l d i n c l u d e t r a n s p o r t t i m e and time elapsed during evaluation in the emergency care facility. Based on the results of this study, it becomes apparent that closer observat i o n of p a t i e n t v e n t i l a t o r y f u n c t i o n while affixed ~:o these devices is indicated. The c o m m o n practice of leaving patients strapped to these boards while in the emergency center could hamper respiratory function. This deleterious effect, when coupled with coexistent traumatic or chronic pulmonary pathology, m a y serve to further compromise the patient's ventilation. A l t h o u g h effective spinal i m m o b i l i zation i n suspected spinal injury patients is mandatory, strap tension may need to be adjusted judiciously so as not to restrict chest wall excursion. CONCLUSION O u r s t u d y d e m o n s t r a t e d t h a t the long spinal board and the ZED board used for spinal i m m o b i l i z a t i o n have restrictive effects on p u l m o n a r y function in the healthy, n o n s m o k i n g man. Further studies are needed on actual patients, but clinicians should consid-
Annals of Emergency Medicine
er this factor as a n o t h e r potential source of respiratory compromise in the traumatized patient.
REFERENCES
l. AbrahamE, GongH, TashkinDP, et ah Effect of pneumatic trousers on pulmonary function. Crit Care Med 1982;I0:754-757. 2. Ranson KJ, McSwain NE: Respiratory function following application of MAST trousers. JACEP 1978;7:297-299. 3. American Thoracic Society: Standardization of spirometry. A m Rev Respir Dis 1979;119: 831-838. 4. Smith AA, Gaensler EA: Timing of forced expiratory volume in one second. Am Rev Respit Dis 1975;112:882-885. 5. Thomas HM, Garrett RC: Interpretation of spirometry -- a graphic and computational approach. Chest 1984;86:I29-131. 6. Zamel N, Altose MD, Speir WA: Statement on spirometry: A report of the section on respiratory pathophysiologz Chest 1983;83:547-550. 7. American Heart Association Council: Manual for evaluation of lung function by spirometry. Circulation 1982;65:644A-651A. 8. Crapo RO, Morris AH, Gardner RM: Reference spirometric values using techniques and equipment that meet ATS recommendations. Am Rev Respir Dis i981;123:659-664. 9. Briscoe WA: Lung volumes, in Fenn WO, Rahn H (eds): Handbook of Physiology: Respiration, section 3, vol 2. Washington,DC, American PhysiologicalSociety, i964, p 1363. 10. Hankinson JL, Gardner RM: Standard waveforms for spirometer testing. Am Rev Respir Dis i982;126:362-364. I1. Pennock BE, Rogers RM, McCaffree DR: Changes in measured spirometricindices: What is significant?Chest 1981;80:97-99.
17:9 September I988
Effect of Spinal Immobilization Devices on Pulmonary Function in the Healthy, Nonsmoking Man In the prehospital management of trauma, a variety of devices are used for immobilization of the spinal column during extrication and transport. Two of these commonly used immobilizers, the Zee Extrication Device ® and the long spinal board, use crisscrossing straps over the thorax to affix the patient to the device. Our study was designed to determine if these two devices alter pulmonary function in the healthy, nonsmoking man. We took 15 healthy, nonsmoking male volunteers and tested four pulmonary function parameters: forced vital capacity (FVC), forced expiratory volume in one second (FEV1), the ratio FEVI:FVC, and forced mid-expiratory flow (FEF 25%-75%). A Breon spirometer was used to test these functions both before and after the volunteers were strapped into the two devices. Three separate trials were given for each parameter and the best scores were used for data computation. Strap tension was controlled by placing a sphygmomanometer beneath each strap and adding tension to produce 10 m m Hg pressure. We found a significant difference (P < .05) between prestrapping and poststrapping values for three of the four functions tested using the long spinal board: FVC (P = .0079), FEV 1 (P = .0001), and FEF 25%-75% (P = .0252). Similarly significant differences were found for three of the four parameters using the Zee Extrication Device®: FVC (P = .004), FEV 1 (P = .0022), and FEF 25%-75% (P = .008). These differences reflect a marked pulmonary restrictive effect. The ratio FEVdFVC can be normal or even slightly elevated with restrictive airway disease due to proportional reductions of each parameter. Correspondingly, we found no significant difference between prestrapping and poststrapping FEVI:FVC values (P > .05). We conclude from our data that these devices produce a significantly restrictive effect on pulmonary function in the healthy, nonsmoking man. [Bauer D, Kowalski R: Effect of spinal i m m o b i l i z a t i o n devices on p u l m o n a r y function in the healthy, nonsmoking man. Ann Emerg Med September 1988;17:915-918.]
David Bauer, MD Robert Kowalski Royal Oak, Michigan From the Department of Emergency Medicine, William Beaumont Hospital, Royal ©ak, Michigan. Received for publication August 17, 1987. Revision received April 18, 1988. Accepted for publication June 1, 1988. Presented at the University Association for Emergency Medicine Annual Meeting in Philadelphia, May 1987. Address for reprints: David Bauer, MD, William Beaumont Hospital, Department of Emergency Medicine, 3601 West Thirteen Mile, Royal Oak, Michigan 48072.
INTRODUCTION In the prehospital management of trauma, a variety of devices are used for immobilization of the spinal column during extrication and transport. Two of these commonly used devices, the Zee Extrication Device ® (ZED) (Zee Medical Products, Irvine, California} (Figure 1) and the long spinal board (Figure 2), use crisscrossing straps over the thorax to affix the patient to the device {Figures 3 and 4}. Our study was designed to determine if these two devices alter pulmonary function in the healthy, nonsmoking man because they are used universally in emergency departments, and their effect on pulmonary function may have clinical significance. No studies have addressed this particular issue. However, Abraham et all used pulmonary function tests to analyze the effects of pneumatic trousers on respiratory function, and Ranson and McSwain 2 also studied respiratory function after pneumatic trouser application but used arterial blood gas measurements. MATERIALS A N D M E T H O D S Study approval was granted by the Human Investigations Committee of William Beaumont Hospital. Study participants were 15 male volunteers 23 to 28 years old who had no history of recurrent respiratory disease, heart 17:9 September 1988
Annals of Emergency Medicine
915/91
SPINAL IMMOBILIZATION DEVICES Bauer & Kowalski
FIGURE 1. ZEE Extrication Device ®. FIGURE 2. Long spinal board.
disease, or current respiratory symptoms (ie, cough, nasal discharge, or c o n g e s t i o n ) , and w h o w e r e n o n smokers. Before participation, a brief physical examination including lung auscultation was performed, and none of the volunteers was observed to have abnormal findings. Volunteers were aware of the mechanics of the study but were not informed of its purpose. Two i m m o b i l i z a t i o n devices were tested in the study. One device, the ZED, is used c o m m o n l y in extrication when spinal immobilization is necessary. It consists of an oblong piece of durable cloth material reinforced with long, thin metal bars. Multiple crisscrossing straps affix the patient's torso to the board. The second device tested was a long spinal board routinely used for patient transport if spinal injury is suspected. It also uses crisscrossing straps across the thorax. The same two boards were used throughout the study. To test the effect of each device on pulmonary function, both control trials and poststrapping trials were conducted. Subjects were placed on each board in the supine position, and pulmonary functions were measured with a Breon spirometer. Measurements included forced vital capacity (FVC), forced expiratory v o l u m e in one second (FEV1), forced midexpiratory f l o w (FEF 2 5 % - 7 5 % ) , a n d t h e FEVI:FVC ratio. Three prestrapping trials were performed on each subject on each board. Testing was done by two respiratory therapists blinded to the purpose of the study and experienced in performing pulmonary function testing. C o a c h i n g t e c h n i q u e s were kept consistent throughout the study. A one-minute rest was allotted between each trial. Results were recorded with the spirometer on a separate piece of graph paper for each trial. After these control trials, the straps were applied to the subjects, and three trials of p u l m o n a r y functions were carried out on each board as outlined above. Strapping was done by the same investigator at all times. Strap tension was regulated by placing a s p h y g m o m a n o m e t e r bladder u n d e r each strap and applying tension until 10 m m Hg was recorded at functional
92/916
TABLE L ZEE extrication device
Parameter
Prestrapping (L/min)
Poststrapping (I./min)
P
FVC
5.41
+_ 0.81
4.78
+ 0.73
.0040
FEV~
4.43
_+ 0.67
3.95
_+ 0.59
.0022
FEF 25%-75%
4.56
+ 1.28
3.90
_+ 0.96
.0080
FEV~:FVC
0.816 _+ 0.05
0.820 _+ 0.04
.6107
Values are mean _+ SD. FVC, forced vital capacity; FEV1, forced expiratory volume in one second; FEF 25%-75%, forced midexpiratory flow; FEVcFVC, ratio of FEVt to FVC.
residual capacity (end-expiration point). This value of 10 m m Hg for strap tension was obtained before the study by having an experienced paramedic blinded to the study strap a volunteer to the board. His strap tension was recorded on three separate occasions (mean, 10 m m Hg). T h e r e s u l t s of p r e s t r a p p i n g and
Annals of Emergency Medicine
poststrapping values for both boards were derived from the graph paper recordings. R e c o m m e n d a t i o n s by the American Thoracic Society for computation of data were used. 3 For each set of three trials, the largest FVC and FEV 1 values were taken for data computation, even if they were from different recordings. Reproducibility of 17:9 September 1988
FIGURE 3. Demonstration of patient
strapped in long spinal board. FIGURE 4. Demonstration of patient strapped in ZED board. inate a c c u m u l a t i o n of Type I errors because pulmonary functions were not independent. This value was significant at P = .0287 and indicated a significant effect by the ZED or long s p i n a l board. I n d i v i d u a l S t u d e n t ' s t tests then were performed on all four p u l m o n a r y functions for each board to isolate significant effects. Finally, to determine if there was a significant difference between the ZED and the spinal boards, Hotelling's T2 m u l t i v a r i a t e analysis was applied to the m e a n vectors.
RESULTS For the ZED board, the values are shown (Table 1}. A significant effect was noted for three of the four pulmonary hmctions: FVC (P = .004), FEV 1 (P = .0022), and FEF 25%-75% (P = .008). FEVI:FVC was not affected significantly {P = .61). For the spinal board, the values are shown (Table 2). The same three pulm o n a r y f u n c t i o n s were affected by strapping: FVC (P = .0001), FEV 1 (P = .0079), and FEF 25%-75% (P = .0252). Again, FEVI:FVC was not significantly altered. N o significant difference in effect b e t w e e n t h e t w o b o a r d s was f o u n d {P = .413) (Table 3) w h e n t h e difference between prestrapping and poststrapping values of each parameter were compared.
TABLE 2. Long spinal board
Parameter
Prestrapping (L/min)
FVC
5.52
FEV 1 FEF 25%-75%
4.29
_+ 0.64
4.11
± 1.12
FEVI:FVC
0.791 ± 0.05
_+ 0.79
Poststrapping (L/min) 4.98
P
± 0.67
.0001
3.99
± 0.57
.0079
3.68
±.1.02
.0252
0.793 ± 0 . 0 5
.8541
Values are mean _+ SD.
FVC and FEV 1 was ensured because the best two of three spirograms for these parameters did not vary by m o r e than 5% of t h e largest v a l u e or b y more than 100 mL. The FEF 25%-75% values then were taken from the tracing with the largest s u m of FVC and FEV1, as r e c o m m e n d e d by the Society.3 T h e b a c k - e x t r a p o l a t i o n t e c h nique as d e s c r i b e d b y S m i t h a n d Gaensler4 was i m p l e m e n t e d to extract 17:9 September 1988
v a l u e s on r e c o r d i n g s in w h i c h t h e steepest slope of the curve did n o t occur at the onset. To determine whether either board had a significant effect (P < .05) on p u l m o n a r y function values, poststrapping values were compared w i t h prestrapping values, and Hotelling's T2 multivariate analysis of variance was performed on the m e a n vectors. This statistical m e t h o d was chosen to elim-
Annals of Emergency Medicine
DISCUSSION The results of this study indicate a restrictive effect on p u l m o n a r y function by both the ZED and the spinal boards. In r e s t r i c t i v e a i r w a y disease (ie, p u l m o n a r y fibrosis, pleuraf fibrosis, or c h e s t w a l l a b n o r m a l i t i e s ) , values for FVC are s i g n i f i c a n t l y reduced, reflecting decreased total lung v o l u m e . S u c h a n effect w a s f o u n d w i t h b o t h devices in this study. Decreases in FEV 1 are m o s t notable in obstructive airway disease, S,6 but because expiratory flow in a m a x i m a l effort is d e p e n d e n t on lung volume, FEV1 m a y be reduced w i t h restrictive abnormalities. 6 U n l i k e t h a t seen w i t h obstructive disease, however, the decrease in FEV 1 seen in restrictive conditions is pro917/93
SPINAL IMMOBILIZATION DEVICES Bauer & Kowalski
p o r t i o n a l to the d e c r e m e n t i n l u n g volume; thus, FEV 1 decreases but a normal or slightly elevated FEVI:FVC results. 6 The findings of a significant decrease in FEV I and a lack of significant change in FEVI:FVC w h e n comparing prestrapping with poststrapping values are consistent with restriction. Finally, w i t h marked restrictive disease, a r e d u c t i o n i n FEF 25%-75% may occur, although not as noticeably as in obstructive disease. Again, a significant lowering of FEF 25%-75% observed in this study is consistent with this cause. Standard p u l m o n a r y function values based on age, sex, and height have been described by various authors.g,7, s By convention, subjects in these studies were either standing or sitting, in contrast to the present study where subjects were tested supine. Nevertheless, 14 of 15 subjects tested supine in this s t u d y had b a s e l i n e p u l m o n a r y function values that were w i t h i n the a c c e p t a b l e range for age, sex, and height, as recommended by the American Thoracic Society for standing or sitting values. This includes an FVC and FEV I more than 80% of predicted values and FEF 25%-75% more than 60% of predicted values. One subject had an FVC of 79% of predicted value. Limitations of this study included study in the laboratory versus a true clinical setting, the small sample size, and an estimation of average strap tension by a b l i n d e d p a r a m e d i c ; these should be noted w h e n interpreting the results of this study. O t h e r i n v e s t i g a t o r s have o u t l i n e d the detrimental effects of the supine position on pulmonary function, presumably related to redistribution of blood flow with subsequent increased p u l m o n a r y v o l u m e . I , 9 Because the purpose of this study was to detect differences in p u l m o n a r y functions induced by these devices, subjects serving as their own controls were tested supine. The practical i m p l i c a t i o n of this is exemplified by analyzing time
94/918
TABLE 3. C o m p a r i s o n o f effect on. p u l m o n a r y
function --
L o n g s p i n a l b o a r d vs Z E D b o a r d
Parameter
Poststrapping- Prestrapping (L/min) Long Board ZED Board
P
FVC
0.532
0.635
0.523
FEV1
0.297
0.477
0.083
FEF 25%-75%
0.407
0.648
O.158
FEV1:FVC
0.002
0.004
0.608
relations i n the clinical setting regarding supine versus sitting positions. Although suspected spinal t r a u m a victims may spend a brief period in the sitting position during extrication with a ZED device, the vast majority of their time while strapped in either of these immobilizers is spent supine. This w o u l d i n c l u d e t r a n s p o r t t i m e and time elapsed during evaluation in the emergency care facility. Based on the results of this study, it becomes apparent that closer observat i o n of p a t i e n t v e n t i l a t o r y f u n c t i o n while affixed ~:o these devices is indicated. The c o m m o n practice of leaving patients strapped to these boards while in the emergency center could hamper respiratory function. This deleterious effect, when coupled with coexistent traumatic or chronic pulmonary pathology, m a y serve to further compromise the patient's ventilation. A l t h o u g h effective spinal i m m o b i l i zation i n suspected spinal injury patients is mandatory, strap tension may need to be adjusted judiciously so as not to restrict chest wall excursion. CONCLUSION O u r s t u d y d e m o n s t r a t e d t h a t the long spinal board and the ZED board used for spinal i m m o b i l i z a t i o n have restrictive effects on p u l m o n a r y function in the healthy, n o n s m o k i n g man. Further studies are needed on actual patients, but clinicians should consid-
Annals of Emergency Medicine
er this factor as a n o t h e r potential source of respiratory compromise in the traumatized patient.
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